Apparatus for controlling an exposure

Abstract

An apparatus for controlling an exposure in an image forming apparatus includes an exposure unit which varys the illumination from an exposure light source in accordance to photoreceptor sensitivity and projects the light reflected onto a photoreceptor, and a light reducing filter adjusting a quantity of light to be projected according to the sensitivity of the photoreceptor. The neutral-density filter may be employed as the reducing filter. Preferably, this filter is movable between a first position in a path of the reflected light and a second position out of the path. The photoreceptor having a thicker photosensitive layer may be used to its long life period.

What is claimed is: 
     
       1. An apparatus for controlling an exposure in an image forming device, comprising: an exposure light source which emits light so as to illuminate a document;   projection means for projecting light reflected from said document onto a photoreceptor;   a detector which detects the sensitivity of said photoreceptor;   a movable light reducing filter which optically adjusts the quantity of light reflected from said document and projected onto said photoreceptor when said movable light reducing filter is located in a path of said light; and   an exposure light controller which electrically adjusts the quantity of light reflected from said document by controlling a voltage to be applied to said exposure light source,   wherein said exposure light controller controls said voltage with said movable light reducing filter located in said light path so as to adjust the quantity of light reflected from said document when the sensitivity detected by said detector is greater than a first predetermined level, and said exposure light controller controls said voltage so as to adjust the quantity of said light reflected from said document with said movable light reducing filter positioned out of said light path when the sensitivity detected by said detector is less than said first predetermined level.   
     
     
       2. The apparatus according to claim 1, wherein said light reducing filter is a neutral-density filter. 
     
     
       3. The apparatus according to claim 1, wherein said voltage is gradually increased in accordance with said sensitivity detected by said detector until said sensitivity detected by said detector corresponds to said first predetermined level. 
     
     
       4. The apparatus according to claim 1, wherein said voltage is decreased when said sensitivity detected by said detector corresponds to said first predetermined level. 
     
     
       5. The apparatus according to claim 4, further comprising an alarm means for indicating the end of a useful lifetime of said photoreceptor when said sensitivity detected by said detector corresponds to a second predetermined level which is lower than said first predetermined level. 
     
     
       6. The apparatus according to claim 5, wherein said voltage is gradually increased in accordance with said sensitivity detected by said detector until said sensitivity detected by said detector corresponds to said second predetermined level. 
     
     
       7. An apparatus for controlling an exposure in an image forming apparatus, comprising: an exposure light source which emits light so as to illuminate a document, wherein the quantity of emitted light from said exposure light source is changed by controlling a voltage applied to said exposure light source;   projection means for projecting light reflected from said document onto a photoreceptor, said projection means including a movable light reducing filter for reducing a quantity of light projected onto said photoreceptor when said light reducing filter is located in a light path, said light reducing filter being movable between a first position which is in said light path and a second position which is out of said light path;   a detector which detects a deterioration of the sensitivity of said photoreceptor;   a controller which controls said voltage in accordance with said deterioration detected by said detector with said movable light reducing filter located in said first position when said deterioration detected by said detector is less than a first predetermined level, and which moves said movable light reducing filter from said first position to said second position when said deterioration detected by said detector corresponds to said first predetermined level, and which controls said voltage in accordance with said deterioration detected by said detector with said movable light reducing filter located in said second position when said deterioration detected by said detector is less than a second predetermined level which is greater than said first predetermined level, and which indicates an end of a useful lifetime of said photoreceptor and interrupts the controlling of said voltage when said deterioration detected by said detector corresponds to said second predetermined level.   
     
     
       8. An image forming apparatus comprising: a light source which emits light and exposes a photoreceptor to form an image on said photoreceptor;   a detector which detects the sensitivity of said photoreceptor; and   an adjustment means for adjusting an exposure amount of said light in accordance with said sensitivity detected by said detector, said adjustment means including an optical filter which reduces said exposure amount and a controller which varies electric power to be applied to said light source,   wherein said adjustment means coarsely adjusts said exposure amount by positioning said filter in a light path and out of said light path, and finely adjusts said exposure amount by controlling said electric power.